3-way stopcocks are known as one type of such medical instruments. A 3-way stopcock includes three tributary tubes that are separated from one another by an angle of, for example, 90°. FIGS. 11(a) and 11(b) shows construction of the conventional 3-way stopcock while FIGS. 12(a)–12(b) and 13(a)–13(b) each illustrates one application of the conventional 3-way stopcock, with (a) in each figure being a plan view and (b) being a cross-section. FIG. 14 shows one application of a construction shown in FIGS. 13(a) and 13(b).
In FIGS. 11(a) and 11(b), a reference numeral 1 denotes a 3-way stopcock, a reference numeral 2 denotes a main body thereof, and reference numerals 5, 6, and 7 each indicates a tributary tube. The tributary tubes 5, 6, and 7 are separated from one another by 90°. A reference numeral 8 denotes a thread formed at an end of each of the tributary tubes 5 and 7 whereas a reference numeral 9 denotes a tapered portion formed on one end of the tributary tube 6. A cap is normally placed over each of the threads 8.
Reference numerals 12, 13, and 14 indicate a valve body, a valve shaft, and a handle, respectively. A reference numeral 16 denotes a T-shaped switching conduit formed through the valve shaft 13. The valve shaft 13 of the valve body 12 is fitted into the main body 2. The flow of infusion fluid is switched from one flow passage to another by turning the valve body 12 through the handle 14 so that the switching conduit 16 communicates with the tributary tubes 5, 6, and 7 in turn. An infusion tube, connected to a source of infusion fluid, is connected to the tributary tube 5 through the thread 8 while another tube, connected to a blood vessel, is connected to the tapered portion 9 of the tributary tube 6.
Referring to FIGS. 12 through 14, reference numerals 10, 20, 22, 23, and 50 denote a septum, a cylinder of a syringe (injection cylinder), a connector, a blunt needle, and a plug (infusion plug), respectively. The plug 50 is connected to the tributary tube 7 through the thread 8. Referring to FIGS. 13(a) and 13(b), a 3-way stopcock 1 includes a septum 10 similar to the one shown in FIGS. 12(a) and 12(b). The septum 10 is placed in a relatively short tributary tube 7. Structure of the connector 22 including the blunt needle 23 will be described later. In FIGS. 12(b) and 13(b), a reference numeral 40 indicates air bubbles. The area containing the air bubbles represents an internal space of the tributary tube 7 (i.e., dead space).
The conventional 3-way stopcock 1 as shown in FIG. 11 is arranged between a patient and a source of infusion fluid so that when the valve body 12 is turned, the flow of infusion fluid is selectively switched from one flow passage to another. However, while the tributary tubes 5 and 6 are in communication with each other for administration of a drug solution, the tributary tube 7, not in use, is left unattended without any sanitary measure being taken except for the above-mentioned cap placed over the thread 8. Accordingly, there is a risk of microbial contamination from the end region of the tributary tube 7. Also, there is a concern that the drug solution remaining within the tributary tube 7, which radially extends away from the main body 2, provides an ideal breeding ground for bacteria.
Among various drug solutions, intravenous hyperalimentation may provide an optimum growth medium for bacteria. In particular, the end region of the syringe 20 is subjected to the possibility of contamination through contact with the surrounding atmosphere or linens each time the syringe 20 is attached to, or removed from, the tributary tube 7 of the 3-way stopcock 1. In addition, the deep hollow construction of the tributary tube 7 makes it difficult to wipe off the remaining solution and sterilize the tube, which often results in insufficient sanitary procedures. For this reason, once bacteria enter the tributary tube 7, it is extremely difficult to prevent their growth.
An approach devised by medical practitioners in an effort to cope with these problems involves use of the 3-way stopcock 1 in conjunction with the plug 50 as shown in FIGS. 12(a) and 12(b). Each of the constructions shown in FIGS. 12(a) and 12(b) and in FIGS. 13(a) and 13(b) includes the septum 10 on one end of the tributary tube 7 for isolation from the surrounding atmosphere and thus preventing entrance of bacteria while the tributary tube 7 is not in use. During use of the tributary tube 7, the septum 10 may be punctured by a syringe needle for, for example, injecting an additional drug solution into the main drug solution. In case of the 3-way stopcock 1 as shown in FIGS. 12(a) and 12(b), the plug 50 is attached to the end of the tributary tube 7. The two components connected to one another have an increased length and, as a result, the volume of the drug solution that the tube can contain is increased by a corresponding amount. This increase in the volume of the flow passage of infusion fluid leads to formation of a dead space in which a small amount of the high concentration drug solution remains. As a result, dosage of the drug solution may fall short, or the drug solution may be wasted. Furthermore, if administration of an additional drug solution follows, the residual solution may be added to the additional solution, which results in an excessive dosage or a mixture of the added drug solution and the residual solution being administered to patients.
In general, when it is desired to collect blood samples during this type of infusion process, the infusion is interrupted to allow blood to flow back to upstream of the 3-way stopcock 1. Once the inrushing blood has filled adjacent area of the 3-way stopcock 1, the septum 10 of the 3-way stopcock 1 is punctured by a syringe needle to collect the undiluted blood. After collection of the blood samples, the infusion fluid is again allowed to flow in the positive direction through the flow passage of infusion fluid to push out the blood toward the blood vessel and clean the flow passage of infusion fluid.
However, the dead space as shown in FIGS. 12(a) and 12(b) impedes collection of blood samples through the septum 10 of the 3-way stopcock 1 using a syringe. This is a particularly serious problem in the case of arterial infusion, in which blood collection is essential. Further, the increased passage length increases generation of air bubbles 40 and makes it considerably difficult to remove the bubbles. In addition, such a dead space makes the deaeration process difficult during the brimming process when the infusion passage is filled with infusion fluid in the first place. Furthermore, the large dead space can provide an ideal breeding ground for bacteria that enter the tube by accident.
In comparison, the 3-way stopcock 1 as shown in FIGS. 13(a) and 13(b) has a short tributary tube 7 and mitigates the problems associated with the dead space as described in reference to FIGS. 11 and 12. In such a construction, however, when the syringe 20 or the connector 22 is connected for side injection or mixed infusion of a drug solution, the needle of the syringe or the connector 22 that punctures the septum 10 and projects into the T-shaped switching conduit 16 interrupts switching operation of the infusion passage. In order to permit switching of the flow passage of infusion fluid, the syringe or the connector 22 must be pulled out each time the flow passage is switched. As a result, not only the advantage of the 3-way stopcock that the infusion passage can be freely switched is lost, but each insertion/removal of the syringe 20 or the connector 22 also increases the likelihood of bacteria entrance. This is also the case with the 3-way stopcock as shown in FIG. 14.